U.S. patent number 9,776,206 [Application Number 14/588,870] was granted by the patent office on 2017-10-03 for method for depositing high aspect ratio molecular structures.
This patent grant is currently assigned to CANATU OY. The grantee listed for this patent is CANATU OY. Invention is credited to David P. Brown, David Gonzales, Esko I. Kauppinen, Albert G. Nasibulin.
United States Patent |
9,776,206 |
Brown , et al. |
October 3, 2017 |
Method for depositing high aspect ratio molecular structures
Abstract
A method for depositing high aspect ratio molecular structures
(HARMS), which method comprises applying a force upon an aerosol
comprising one or more HARM-structures, which force moves one or
more HARM-structures based on one or more physical features and/or
properties towards one or more predetermined locations for
depositing one or more HARM-structures in a pattern by means of an
applied force.
Inventors: |
Brown; David P. (Espoo,
FI), Nasibulin; Albert G. (Espoo, FI),
Kauppinen; Esko I. (Helsinki, FI), Gonzales;
David (Helsinki, FI) |
Applicant: |
Name |
City |
State |
Country |
Type |
CANATU OY |
Espoo |
N/A |
FI |
|
|
Assignee: |
CANATU OY (Espoo,
FI)
|
Family
ID: |
36191905 |
Appl.
No.: |
14/588,870 |
Filed: |
January 2, 2015 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20150209823 A1 |
Jul 30, 2015 |
|
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
12281888 |
|
8951602 |
|
|
|
PCT/FI2007/000059 |
Mar 7, 2007 |
|
|
|
|
Foreign Application Priority Data
|
|
|
|
|
Mar 8, 2006 [FI] |
|
|
20060227 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B82Y
40/00 (20130101); B05D 1/04 (20130101); B82B
3/00 (20130101); B82Y 30/00 (20130101); C01B
32/15 (20170801); Y10S 977/845 (20130101); Y10S
977/742 (20130101); Y10S 977/84 (20130101); Y10S
977/842 (20130101) |
Current International
Class: |
B82Y
10/00 (20110101); B05D 1/04 (20060101); B82B
3/00 (20060101); B82Y 30/00 (20110101); B82Y
40/00 (20110101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
02/03430 |
|
Jan 2002 |
|
WO |
|
03/084869 |
|
Oct 2003 |
|
WO |
|
2004/015786 |
|
Feb 2004 |
|
WO |
|
2005/007565 |
|
Jan 2005 |
|
WO |
|
2005/041227 |
|
May 2005 |
|
WO |
|
2005/061382 |
|
Jul 2005 |
|
WO |
|
2005/065425 |
|
Jul 2005 |
|
WO |
|
2005/085130 |
|
Sep 2005 |
|
WO |
|
2005/085131 |
|
Sep 2005 |
|
WO |
|
WO 2005085130 |
|
Sep 2005 |
|
WO |
|
2006/099749 |
|
Sep 2006 |
|
WO |
|
2006/125457 |
|
Nov 2006 |
|
WO |
|
2006/138263 |
|
Dec 2006 |
|
WO |
|
Other References
Washington, Particle Size Analysis in Pharmaceutics and Other
Industries: Theory and Practice, Taylor & Francis, (1992), pp.
167. cited by examiner .
The extended European Search Report including the Supplementary
European Search Report and European Search Opinion;
EP07712601.9-1508; Dec. 20, 2013. cited by applicant .
International Search Report for Application No. PCT/FI2007/000059,
dated Jun. 25, 2007. cited by applicant .
Finnish Search Report; FI20060227; Jan. 19, 2001. cited by
applicant .
Finnish Search Report; FI20060227; Oct. 4, 2007. cited by applicant
.
Finnish Office Action; FI20060227; May 22, 2008. cited by applicant
.
Kim, S.H. et al., "In-flight size classification of carbon
nanotubes by gas phase eletrophoresis", Institute of Physics
Publishing, Nanotechnology 16 (2005) pp. 2149-2152. cited by
applicant .
Dong, Lifeng et al., "Floating-Potential
Dielectrophoresis-Controlled Fabrication of Single-Carbon-Nanotube
Transistors and Their Electrical Properties", J. Phys. Chem. B
2005, 109, pp. 13148-13153. cited by applicant .
Krinke T. J. et al.; "Positining of nanometer-sized particles on
flat surfaces by direct deposition from the gas phase"; Applied
Physics Letters; Jun. 4, 2001; vol. 78 No. 23; pp. 3708-3710;
American Institute of Physics; Melville, NY. cited by applicant
.
Welle A. et al.; "Pringting of organic and inorganic nanomaterials
using electrospray ionization and Coulomb-force-directed assembly";
Applied Physics Letters; Dec. 29, 2005; vol. 87 No. 26; pp.
263119-263119, American Institute of Physics; Melville, NY. cited
by applicant .
Washington; Particle Size Analysis in Pharmaceutics and Other
Industries; Theory and Practice, Taylor & Francis; 1992; p.
167. cited by applicant .
Chad R. Barry et al., "Nanoparticle Assembly by Nanoxerography",
Proceedings of the 2004 NSF Design, Service and Manufacturing
Grantees and Research Conference, Jan. 5, 2004, Department of
Electrical and Computer Engineering, University of Minnesota. cited
by applicant .
Summons to attend oral proceedings pursuant to Rule 115(1) EPC
issued by the European Patent Office on Sep. 29, 2016, which
corresponds to European Patent Application No. 07712601.9-1504 and
is related to U.S. Appl. No. 14/588,870. cited by
applicant.
|
Primary Examiner: Jiang; Lisha
Attorney, Agent or Firm: Studebaker & Brackett PC
Claims
The invention claimed is:
1. A method for depositing high aspect ratio molecular structures
(HARM-structures), the method comprising: providing an aerosol
comprising individual and bundled HARM-structures; applying a force
upon the individual and bundled HARM-structures; moving at least
part of the individual and bundled HARM-structures based on one or
more physical features and/or properties towards one or more
predetermined locations by means of the applied force; and
depositing at least part of the individual and bundled
HARM-structures in a pattern by means of the applied force, wherein
the force is a thermophoretic force, and one or more individual and
bundled HARM-structures are deposited in the pattern by patterned
heating and cooling of a collection plate.
2. A method according to claim 1, wherein the individual and
bundled HARM-structures comprise at least one selected from a
carbon nanotube, a fullerene functionalized carbon nanotube, a
boron-nitride nanotube, a nanorod including carbon, a phosphorous-,
boron-, nitrogen- or silicon-containing nanorod, a filament, a
tube, a rod and ribbon.
3. A method according to claim 2, wherein the method further
comprises adding one or more reactants, agents, coating materials,
functionalizing materials, surfactants and/or dopants to the
aerosol comprising individual and bundled HARM-structures.
4. A method according to claim 1, wherein the method further
comprises adding one or more reactants, agents, coating materials,
functionalizing materials, surfactants and/or dopants to the
aerosol comprising individual and bundled HARM-structures.
Description
The invention relates to a method for moving High Aspect Ratio
Molecular Structures (HARMS) and to the use of the method.
PRIOR ART
High aspect ratio molecular structures (HARMS) are promising
building blocks for devices from the nanoscale upwards due to their
small size and their unique, nearly one-dimensional morphology.
Examples of HARM-structures include nanotubes (NTs) for example
carbon nanotubes (CNTs), fullerene functionalized carbon nanotubes
(FFCNTs), boron-nitride NTs (BNNTs), nanorods including carbon,
phosphorous, boron, nitrogen and silicon containing nanorods,
filaments and other tubular, rod, or ribbon or otherwise high
aspect ratio molecular structures.
HARMS-based architectures such as field-effect transistors, field
emission displays, memory devices, quantum wires and logic gate
circuits have already been demonstrated. For further progress and
wider application, however, the development of methods for the
controllable and economical synthesis, separation, collection,
deposition, patterning and incorporation into devices of
HARM-structures are extremely desirable. In particular, many
applications of HARM-structures require largely individual (i.e.
unbundled) HARM-structures to be in gaseous, liquid or solid
dispersions or as a deposit on a surface in the form a layer, film,
patterned deposit or three dimensional structure.
However, a problem is that due to strong intermolecular forces
(such as van der Waals and Coulomb) many types of HARM-structures
spontaneously form bundles during their synthesis, transport and/or
storage. For example, production of CNTs by carbon-arc discharge,
laser ablation and/or high pressure CO processes is associated with
a high degree of tube bundling.
Methods to selectively produce isolated HARM-structures in
dispersions, layers, films, or structures are known in the art.
However, a problem with prior art methods is that separation of
isolated HARM-structures typically requires separate synthesis,
purification, functionalization and/or deposition steps
necessitating the utilization of surfactants, polymers, peptides or
other compounds to exfoliate the bundles and extract individuals.
Such processes may significantly alter the original properties of
the HARM-structures and are expensive, time consuming and
inefficient.
Methods such as supported chemical vapor deposition (CVD) have been
used for the direct synthesis of isolated HARM-structures on
surfaces. However, the requirement of using high growth
temperatures and/or specific surface reactivity inevitably limits
the use of temperature sensitive or reactive substrate materials
(e.g. polymers) and inhibits the simple integration of the
HARM-structures into, for example, nanoscale electronic devices,
conductive films or structural composites.
The objective of the present invention is to eliminate the
drawbacks referred to above.
An object of the present invention is to provide a new method for
depositing HARM-structures. An object of the present invention is
to improve the efficiency of use of synthesis materials and product
yield, reduce or eliminate the degradation of HARM-structures
during processing, permit the separation of bundled and individual
HARM-structures and allow low temperature homogeneous or patterned
deposition on a wide variety of substrates that would be highly
beneficial to industry and commerce.
SUMMARY OF THE INVENTION
The method and its use are characterised by what has been presented
in the claims.
The invention is based on research work carried out in which it was
surprisingly found that HARM-structures have particular useful
properties.
The term HARM-structure (high aspect ratio molecular structure) is
meant to include, but not be limited to, a nanotube, a carbon
nanotube, a fullerene functionalized carbon nanotube, a
boron-nitride nanotube, a nanorod including carbon, phosphorous,
boron, nitrogen and/or silicon containing nanorod, a filament
and/or any other tube, tubular, rod and/or ribbon and/or any other
high aspect ratio molecular structure in, for example, individual
or bundled form. In other words, by one or more HARM-structures can
be meant one or more different and/or similar HARM-structures. By
one or more HARM-structures can be meant one or more similar
HARM-structures, for example carbon nanotubes, for example, in
bundled and/or individual form.
One particular property of HARM-structures is the spontaneous
charging of bundles of HARM-structures and the electrical
neutrality of the individual HARM-structures. During the synthesis
process, and in the absence of any additional charging, for
example, bundled CNTs largely carry a net electric charge while
individual CNTs are largely uncharged. Similar behavior occurs in
all HARM-structures since they are substantially one-dimensional
structures and have a high fraction of surface atoms available for
direct contact with neighboring HARM-structures, which gives rise
to the charging. This charging phenomenon can be used to move (for
example accelerate), separate and/or deposit one or more
HARM-structures, for example individual and/or bundled
HARM-structures. Also different other properties of the
HARM-structures can be used to, for example, separate bundled and
individual HARM-structures from each other and/or for depositing
said structures. For example, the increased mass of bundled
HARM-structures relative to individuals can be used to separate
them via their differing ratio of inertial to drag forces. This
ratio is determined by the Stokes number (St) defined as St=(.rho.
d U)/(18 .mu.L), where .rho. is the effective density of the
individual or bundled HARM-structure, d is the effective diameter
of the bundled or individual HARM-structure, U is the carrier fluid
speed, .mu. is the carrier fluid viscosity, and L is the
characteristic dimension of the channel or jet. Bundled
HARM-structures exhibit higher stokes numbers than individual.
The present invention relates to a method for depositing high
aspect ratio molecular structures (HARMS), in which method a force
is applied upon an aerosol comprising one or more HARM-structures,
which force moves one or more HARM-structures based on one or more
physical features and/or properties towards one or more
predetermined locations for depositing one or more HARM-structures
in a pattern by means of an applied force.
In other words, the force moves said one or more HARM-structures in
one or more predetermined directions. The force can, for example,
move bundled structures but not the individual ones. Also, the
force can selectively move specific previously charged
structures.
By an aerosol can be meant that one or more HARM-structures are in
a gaseous phase. By an aerosol can be meant a dispersion of one or
more HARM-structures in a gaseous supporting medium.
By a pattern is meant any desired form into which HARM-structures
can be deposited. A pattern can be for example in the form of a
symbol, a region, a letter, a text, an arrow, a straight line, a
circle, a rectangle and/or any other graphic image and/or figure. A
pattern can be in the form of any desired structure and/or
dimensional form. The pattern can be in the form of a layered
structure. The pattern can be for example in the form of a layer
and/or film. The pattern can be in the form of a desired patterned
stamp and/or mask. The pattern can be in the form of a grid and/or
array of connected and/or unconnected elements. The pattern can be
in the form of a three dimensional patterned multi-layer structure.
In one embodiment of the present invention the force is applied
upon one or more bundled HARM-structures. In one embodiment of the
present invention the force is applied upon one or more individual
HARM-structures. In one embodiment of the present invention the
force is applied upon one or more bundled and individual
HARM-structures, wherein the force moves the bundled and/or the
individual HARM-structure based on one or more physical features
and/or properties. In this way one or more bundled and/or
individual HARM-structures can be moved to one or more
predetermined locations where the deposition takes place.
The physical feature and/or property can be, for example, the
charge and/or mass of the HARM-structure and/or any other feature,
for example property, based on which a specific HARM-structure is
acted upon and thereby moved by the force. By a physical feature
and/or property is meant any naturally occurring feature and/or
property of the HARM-structure and/or any feature, for example
property, that has been given the HARM-structure. For example, the
HARM-structure can be charged by any suitable means before and/or
during the performing of the method according to the present
invention. For example, in addition and/or alternatively to the
natural charge of the bundled and to the natural neutral charge of
individual structures, one or more desired specific HARM-structures
can be charged using any suitable manner before performing the
method. In this way, for example, individual naturally uncharged
HARM-structures can also be charged, for example to enable their
deposition. Also both bundled and individual HARM-structures can be
charged in order to provide them the desired physical feature so
that both react to the force applied. Preferably such a physical
feature and/or property based on which the force moves one or more
HARM-structures is a charge, either a naturally occurring charge or
a provided charge.
In one embodiment of the present invention the method is performed
as a step after the synthesis and/or production of HARM-structures.
In other words the HARM-structures can be produced before
performing the method according to the invention and/or can be
produced as a continuous process with the method according to the
present invention. The method according to the present invention
can also be performed in the production step of HARM-structures.
However, already synthesized HARM-structures are used in the
method. In other words, already synthesized or produced
HARM-structures are deposited.
A force can be applied upon a dispersion, for example a mixture,
which comprises one or more bundled and individual HARM-structures,
wherein the force moves the bundled and/or the individual
HARM-structure based on one or more physical features and/or
properties for substantially separating the bundled and individual
HARM-structures from each other. Preferably the force moves
substantially either the bundled or the individual
HARM-structure.
HARM-structures can be formulated as a dispersion in a gas, a
dispersion in a liquid, a dispersion in a powder and/or a
dispersion in a solid. Said dispersion, for example mixture, can be
suspended in a gas phase as an aerosol, suspended in a liquid as an
aquasol, suspended in a granular and/or powder media, a glass
and/or a solid and/or exist in a vacuum.
The HARM-structures, for example as a dispersion, can, for example,
be introduced into an electrical force field, wherein the naturally
charged bundled HARM-structures move or accelerate in the electric
field while individual HARM-structures are substantially
unaffected. In other words, said force selectively moves the
bundled and/or individual HARM-structures relative to one another
so that in this way the bundled and individual HARM-structures are
separated and/or isolated.
One or more HARM-structures can be deposited in a gaseous, liquid,
and/or solid dispersion and/or matrix and/or on a surface as a
layer, pattern and/or structure.
In one embodiment of the present invention, for example bundled or
individual HARM-structure can be deposited. For example separated
bundled and/or individual HARM-structure can be deposited. For
example bundled and individual HARM-structures can be deposited.
For example, a dispersion of bundled and individual HARM-structures
can be deposited.
For example, previously separated, bundled HARM-structures can be
deposited on a surface, if desired. For example, in this way it is
possible to remove said HARM-structures from the dispersion and to
collect them for further use. Said HARM-structures can also, if
desired, be made to remain as a dispersion and in that way generate
two dispersions comprising bundled and individual HARM-structures,
respectively.
Different types of forces can be used in the method according to
the present invention. The force moving and, for example, further
depositing the one or more HARM-structures, can be an electrical,
an electrostatic, a magnetic, an inertial, an acoustic, a viscous,
a photophoretic, a thermophoretic, and/or gravitational force.
Different kinds of forces can be combined. Forces can be combined
to include, for example, inertial impaction, gravitational settling
and acoustic focusing.
In one embodiment of the present invention the HARM-structure is a
naturally charged or uncharged structure. In one embodiment of the
present invention the HARM-structure is positively, negatively or
neutrally-charged (zero-charged). In one embodiment of the present
invention the HARM-structure is provided a charge using any
suitable process.
In one embodiment of the present invention the force moving the one
or more HARM-structures comprises an electrical force moving the
naturally charged bundled HARM-structure. In one embodiment of the
present invention the force comprises an inertial force, which acts
upon and thereby preferably moves the bundled HARM-structure.
In one embodiment of the present invention the electrical force
moving the one or more HARM-structures is provided by means of an
electrostatic force, i.e. an electrical field. The electrostatic
force can be provided, for example, by means of contacting a
conductive material to a non- or semiconducting substrate so as to
charge the surface of the substrate, whereby one or more similar
and/or different HARM-structures having a given electrical charge
move towards the region of the surface having the opposite charge.
The conducting material can have a form of a patterned stamp or
mask. This patterned stamp or mask can be transferred to the non-
or semiconducting material surface by contact charging. The desired
HARM-structure only move towards the charged pattern, where it is
deposited thereby forming a patterned deposition of
HARM-structures.
Further, the force for moving, for example accelerating, and/or
further depositing can be a thermophoretic force. A thermophoretic
force can be provided, for example, by means of a heated plate or
surface in proximity to a parallel cooled plate or surface so as to
cause the desired one or more HARM-structures to move in the
direction of the cooled plate or surface. Furthermore, the cooled
plate can be heated in predetermined regions so as to form a
pattern of alternatively hot and cold regions and thus cause the
desired one or more HARM-structures to move to the cold regions
thereby forming a patterned deposition of HARM-structures. It is
also possible to place a substrate between said cooled plate or
surface and dispersion/mixture of HARM-structures so as to cause
the desired one or more HARM-structures to move to the cold regions
thus forming patterned deposition on the substrate.
In one embodiment of the present invention one or more reactants,
agents, coating materials, functionalizing materials, surfactants
and/or dopants can be added to the one or more HARM-structures, for
example, to a dispersion of bundled and individual HARM-structures,
to bundled HARM-structures or to individual HARM-structures. In
this way it is possible to, for example, modify the HARM-structure
prior to deposition and/or, for example, form a composite or
functionalized material or otherwise modify the one or more
HARM-structures prior to deposition.
Separated dispersed individual and/or bundled HARM-structures can
be deposited by the method according to the present invention on
and/or in a surface, film and/or solid, liquid and/or gaseous
dispersion and/or matrix material. HARM-structures can also be
oriented, coated, functionalized and/or otherwise modified before
and/or after they are for example deposited and/or collected. The
bundled and/or individual HARM-structures can be deposited in a
pattern and/or structures in defined locations.
Further, various means can be used to increase the efficiency of
deposition of the HARM-structures including, but not limited to,
electrophoresis, magnetophoresis, thermophoresis, inertial
impaction, gravitational settling, photophoresis, acoustic focusing
and/or some other similar means.
HARM-structures, for example HARM-structure composites, can be
formulated as a dispersion in a gas, liquid, solid, powder, paste
and/or colloidal suspension and/or they can be deposited on a
surface.
The present invention further relates to the use of the method in a
continuous or batch process for the production, separation,
modification, deposition and/or further processing of one or more
HARM-structures.
The present invention further relates to the use of the method
according to the present invention in the preparation of a
functional material.
The present invention further relates to the use of the method
according to the present invention in the preparation of a thick or
thin film, a line, a wire, a pattern, a layered and/or three
dimensional structure.
The present invention further relates to the use of the method
according to the present invention in the preparation of a device.
The device can, for example, be an electrode of a capacitor, a fuel
cell or battery, a logical gate, an electro-mechanical actuator, an
inverter, a probe or sensor, a light source or diode, a thermionic
power supply, a field effects transistor, a heat sink or heat
spreader, a metal-matrix composite or polymer-matrix composite in a
printed circuit, a transistor, a carrier for drug molecules or
electron emitter in a field emission display. The device can
further be any other device in which preparation the method
according to the present invention can be used.
An advantage of the method according to the present invention is
that it can be performed as a continuous and/or batch process.
Further, the method allows in situ separation of individual
HARM-structures and bundles of HARM-structures in the presence or
absence of a supporting media.
An advantage of the method according to the present invention is
that it does not require the use of high substrate temperatures or
surface reactivity and does not require that the HARM-structures to
be synthesized in the same position where they are deposited. In
this way the method allows a wide range of previously unavailable
substrates and/or synthesis methods to be used for material,
component or device manufacture. The advantage is that the
separation can be followed by the dispersion, homogenous and/or
patterned deposition of said HARM-structures on a wide variety of
substrates without any temperature and/or reactivity limitation.
For example, since collection can be carried out at ambient
temperature, this enables the deposition of individual or bundled
CNTs, for example, on a wide variety of substrates, including those
substrates which cannot withstand elevated processing temperatures.
The method further allows the HARM-structures to be synthesized in
a location different from where they are separated, deposited,
collected and/or patterned thus allowing the use of a wide range of
substrates, patterning and/or synthesis methods.
A further advantage is that the HARM-structures can be directly
deposited on a surface as a film or layer or in a three dimensional
structure or in a gaseous, liquid or solid dispersion. The
HARM-structures can also be directly deposited in a patterned
and/or layered deposition on a surface or in a three dimensional
patterned multi-layer structure which can be incorporated into HARM
based devices.
Further, the separation and/or deposition processes can be directly
combined with, for example, HARM-structure synthesis processes.
Hereby, the method according to the present invention can be
combined into a continuous process for the production of
HARM-structure based dispersions, films, patterns and layered
structures. In other words, the method according to the present
invention can be part of a comprehensive process, which can
comprise several different steps including, but not limited to, the
synthesis of HARM-structures, the separation of different kinds of
HARM-structures, their deposition and reuse of unused reagents, for
example, in the synthesis of HARM-structures.
LIST OF FIGURES
In the following section, the invention will be described in detail
by means of embodiment examples with reference to accompanying
drawings, in which
FIG. 1 illustrates one embodiment of the present method for moving
HARM-structures and thereby separating bundled from individual
HARM-structures.
FIG. 2a illustrates one embodiment of the present method for
continuously separating and selectively depositing bundled
HARM-structures.
FIG. 2b illustrates one embodiment of the present method for batch
separation and selective deposition of bundled HARM-structures.
FIGS. 3a, 3b and 3c illustrate other embodiments of the present
method for separating and selectively depositing bundled from
individual BARM-structures.
FIG. 4 illustrates one embodiment of the present method for
depositing individual EARM-structures.
FIG. 5 illustrates one embodiment of the present invention for
patterned deposition of mixed bundled and individual, only bundled
and/or only individual HARM-structures.
FIG. 6 illustrates one embodiment of the present method for
deposition of mixed bundled and individual, only bundled and/or
only individual HARM-structures by thermophoresis.
FIGS. 7a and 7b illustrate other embodiments of the present
invention for patterned deposition of mixed bundled and individual,
only bundled and/or only individual HARM-structures by
thermophoresis.
FIG. 8 illustrates a continuous process for the synthesis and
further processing of HARM-structures.
FIG. 9a, illustrates mobility size distribution (measured using DMA
without .sup.241Am bipolar charger) of the positively and
negatively naturally charged fraction of bundled CNTs in the gas
phase; FIG. 9b illustrates TEM image of the as-grown bundled
CNTs.
FIG. 10a illustrates comparison between the mobility size
distributions of all and neutral CNTs and catalyst particles at
different CO concentrations and FIG. 10b illustrates charged
fraction of particles (N.sup.+/-) and particle number concentration
plotted versus the CO concentration.
FIG. 11a illustrates comparison between the mobility size
distributions of all and neutral CNTs and catalyst particles at
different hot wire heating powers and FIG. 11b illustrates charged
fraction of aerosol particles (N.sup.+/-) and particle number
concentration plotted versus the hot wire heating power.
FIG. 12a illustrates TEM images of individual CNTs and FIG. 12b
illustrates TEM images of both individual and bundles CNTs.
FIG. 13a illustrates AFM images of individual CNTs deposited onto a
temperature sensitive polymer-based substrate (SU-8; 10 jam thick
layer) and
FIG. 13b illustrates AFM images of individual CNTs deposited onto a
Si.sub.3N.sub.4 substrate (119 .mu.m thick layer).
FIG. 14 illustrates AFM image of individual CNTs deposited on a
Si.sub.3N.sub.4 membrane grid.
FIG. 15 illustrates AFM image of individual CNTs deposited on a
SiO.sub.2 substrate.
FIGS. 16 (a and b) illustrates a SEM image of bundled CNTs
deposited on a silica substrate at two different locations where an
electrostatic charge was applied.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 illustrates one embodiment of the present method for moving
and thereby separating bundled from individual HARM-structures. A
mixture of bundled and individual HARM-structures (1) is
collectively subjected to a force (2) which selectively acts on
either the bundled or individual HARM-structures, based on at least
one of their physical features, for example properties,
distinguishing them, such that they are moved, for example
accelerated, relative to one another so as to become separated in
space into a plurality of individual (3) and bundled (4)
HARM-structures.
FIG. 2a illustrates one embodiment of the present invention,
wherein a mixture of bundled and individual HARM-structures (1) is
suspended in, for example, a carrier gas, a liquid or is suspended
in a vacuum. Said dispersion is caused to pass through an electric
field due to a voltage differential (6). Since bundled
HARM-structuresare naturally substantially charged and the
individual HARM-structures are substantially uncharged, the
electric field causes the bundled HARM-structures (4) to migrate in
the electric field (the direction dependant upon the sign of their
net charge) and be separated from the individual HARM-structures
(3), which pass through the electric field largely unaffected. In
other words, the naturally charged HARM-structures are accelerated
toward the channel walls (9) while the individual HARM-structures
exit the channel.
Similarly, FIG. 2b illustrates the method performed in batch mode,
wherein the dispersion of bundled and individual HARM-structures
(1) is put in a chamber (13), wherein an electrical potential or a
voltage (6) is applied to cause the separation and deposition of
bundled (4) and individual (3) HARM-structures. Naturally charged
bundled HARM-structures are accelerated toward the walls (9) while
the individual HARM-structures remain suspended.
FIG. 3 illustrates another embodiment of the present method,
wherein the mixture of bundled and unbundled HARM-structures (1)
are suspended in a liquid or gas and subjected to a force, in this
case an inertial or gravitational acceleration, thus causing the
bundled (4) and individual (3) HARM-structures to separate. Here,
bundled HARM-structures are selectively deposited from individual
HARM-structures and a suspension of individual HARM-structures is
generated via balancing inertia and drag. The dispersion is, in
this embodiment, introduced into a curved channel (9) a) or
directed towards a surface (4) b) and the bundled HARM-structures
having a higher effective Stokes number are accelerated toward the
surface while the individual HARM-structures remain suspended.
Furthermore, the bundled HARM-structures can be made to deposit on
a substrate. Alternatively c), the dispersion of individual and
bundled HARM-structures (1) is fed into an expanding channel (7) in
the opposite direction to the acceleration of gravity (8). The
velocity of the suspending liquid or gas is decreased in the
expanding volume. Thereby, the individual HARM-structures (3)
having a lower Stokes number than the bundled HARM-structures (4)
are carried further up the channel than the bundled
HARM-structures, thereby causing them to separate.
FIG. 4 illustrates that for example separated individual
HARM-structures (3) can be deposited on a separate substrate (9) by
electrostatic precipitation. Herein a voltage (11) is applied to a
needle (12) to create an electron cloud, which charges the
previously uncharged individual HARM-structures. In this device,
HARM-structures are charged by field charging using a corona
discharge that ionizes the gas and creates a small current between
two plates. Thereafter, the use of a force, in this case an
electrostatic migration velocity, will make them to deposit on the
grounded collection plate (10) where the substrate (9) is located.
Moreover, the deposition location can be determined by local
variation of the electric field, thus allowing patterned
deposition. Various means are available for the localization of the
electric field.
FIG. 5 illustrates one way of allowing patterned deposition by use
of an electrostatic force. A pattern of charge can be localized on
a semi or nonconductive substrate (9) by, for example, making a
stamp or mask of conductive material (14) and applying the mask to
the substrate so as to contact charge those areas of the substrate
in contact with the stamp or mask (15). After the stamp or mask is
removed, the contacted areas remain charged and a dispersion of a
mixture of bundled and individual (1), bundled (4) or individual
(3) HARM-structures are then brought into the vicinity of the
charged substrate whereupon the local electric field causes those
with an opposite charge to accelerate toward the predetermined
pattern and to deposit according to the pattern of the stamp or
mask. The resolution of the deposition pattern is thus
approximately equal to that of the stamp or mask.
FIG. 6 illustrates one embodiment of the present invention, wherein
a thermoforetic force is used to deposit HARM-structures (1,3,4) on
a substrate. A notable advantage of depositing particles using the
thermophoretic precipitator is the possibility of employing any
type of substrates. Here, an aerosol of carrier gas and
HARM-structures is made to pass between a gap between a heated
plate (16) and a cooled plate (17). Various means known in the art
can be used to heat and cool the plates, but in the preferred
embodiment, the hot plate is heated via an electric current and the
cold plate is cooled conductively via a flow of cold water. The
HARM-structures then migrate from the hot plate to the cold and are
deposited on the attached substrate (9).
FIG. 7a illustrates a way of depositing HARM-structures, wherein
the HARM-structures are deposited in a pattern by patterned heating
and cooling of the collection plate. Here a plurality of heating
(18) and cooling (19) elements are positioned on one side of the
substrate (9) and the aerosol of mixed, bundled and/or individual
HARM-structures (1,3,4) are introduced on the other side of the
substrate and between a heating plate (16). The HARM-structures are
then deposited by the thermophoretic force, i.e. thermophoresis,
onto the relatively cooler portions of the substrate. Other means
can be used to create the heating and cooling patterns on the
substrate. For example, for low heat conducting substrates,
radiation (for example laser irradiation) can be used. For example,
a pattern of laser beams can be directed toward the cooled
substrate to heat particular regions. The method according to the
present invention can be used to deposit HARM-structures having
different properties to be deposited in different positions as is
illustrated in FIG. 7b. Here, at time interval 1 (t1), the heating
and cooling of the substrate is in a given pattern whereupon the
HARM-structures of type 1 are deposited. Subsequently, the heating
and cooling of the substrate is changed and HARM-structures of type
2 are deposited. The process can be repeated to create complex,
multi-property deposition patterns.
FIG. 8 illustrates the incorporation of the method according to the
present invention into a HARM-production process. In FIG. 8 the
method according to the present invention is incorporated into a
floating catalyst HARM production process known in the art. Here,
catalyst particles or catalyst particle precursors (20) are
introduced into a HARM reactor (21) together with appropriate
source(s) (22) and additional reagents (23) as required. An aerosol
of HARM-structures exit the reactor and are separated in a
separation apparatus (24) which operates according to any of the
methods described to separate bundles (4) and individual (3)
HARM-structures. Thereafter, the individual HARM-structures can be
charged, coated, functionalized or otherwise modified in a
conditioning reactor (25) and then deposited on a substrate (9) in
a deposition reactor (27) according to any of the methods described
to move bundled and/or individual HARM-structures. The deposition
layer can be homogeneous layered or patterned according to the
methods described in the invention. Furthermore, the deposition
layer can be further processed in any suitable way. Further, unused
precursors and/or reagents can be recovered in a recovery reactor
(30) by means known in the art and fed back into the production
cycle. The process can be repeated.
EXAMPLES
In the following examples, bundled and individual HARM-structures,
in this example carbon nanotubes (CNT), were moved and thereby
separated from each other and separately deposited according to the
described invention.
In all examples, the CNTs were continuously synthesized upstream of
the separation and deposition steps to produce an aerosol
containing a mixture of bundled and individual CNTs. A hot wire
generator (HWG) method was used for the synthesis of CNTs as is
known in the art. In the method Fe catalyst particles were produced
by vaporization from a resistively heated catalyst wire in a
H.sub.2/Ar (with a 7/93 mol ratio) flow (400 cm.sup.3/min).
Particles were formed and grown by vapor nucleation, condensation
and particle coagulation processes. Subsequently, the produced
particles were introduced into a ceramic tubular reactor at about
400.degree. C., mixed with a carbon monoxide (CO) flow of 400
cm.sup.3/min and heated to induce CNT formation (from 700.degree.
C. to 900.degree. C.). A porous tube dilutor (6 l/min) was
installed downstream of the reactor to prevent the product
deposition on the walls. 12 cm.sup.3/min of CO.sub.2 was introduced
in the reactor as an etching agent. Unless otherwise stated, all
the experiments were carried out using a heating power to the wire
of 19 W, a CO concentration of 53% in a CO/(Ar--H.sub.2) (93-7 mol
ratio) mixture, and a peak reactor temperature of 700.degree. C.
Mobility size distributions of aerosol particles (i.e. catalyst
particles, individual CNTs and CNT bundles dispersed in the gas
phase) were measured by a differential mobility analyzer system
consisting of a classifier, a condensation particle counter, and an
optional .sup.241Am bipolar charger. Adequate power supplies for
applying both positive and negative polarity to the internal
electrode were used, while the external electrode was kept
grounded. An electrostatic filter (ESF) was located downstream of
the reactor and used to filter out the charged aerosol particles
(when required). The ESP is comprised of two metallic plates with
dimensions of 15 cm, length, and 2 cm, height, separated each other
by a distance of 1 cm. This device enabled the filtering out of
charged aerosol particles by connecting one of the plates to high
voltage (around 4000 V) while the other one was kept grounded.
Aerosol particles including catalyst particles and CNT
HARM-structures were collected on carbon coated copper grids for
their structural characterization by TEM.
Example 1
Moving and Separation of Bundled and Individual CNT HARM-structures
by Electrostatic Precipitation by Taking Advantage of the Naturally
Charging of Bundled HARM-structures
The mobility size distribution of the naturally charged aerosol
particles (i.e. obtained without external bipolar charger prior the
DMA) is illustrated in FIG. 9. The figure shows the dependence of
the measured frequency on both the equivalent mobility diameter, D,
calculated assuming a spherical shape and a single charge, and the
inverse electrical mobility, 1/Z. As can be seen, a broad mobility
distribution with a mean mobility diameter of around 45 nm was
obtained regardless the polarity of the bias and was attributed to
the presence of CNTs. TEM observation of the sample produced at
700.degree. C. and directly collected onto the TEM grid from the
gas phase showed that the nanotubes were single-walled and clearly
aggregated in bundles (FIG. 9b). Since the DMA can classify only
charged aerosol particles, these results indicate that the
nanotubes coming from the reactor were naturally electrically
charged. Furthermore, this phenomenon was observed independently of
the polarity applied to the DMA. According to concentration
measurements, the CNTs were approximately equally positively and
negatively charged with fractions of N.sup.+=47% and N.sup.-=53%,
respectively (table 1).
Previous investigations on metal nanoparticle formation by a HWG
indicated that the particles posses electrical charges after their
formation. In order to study the possibility that Fe catalyst
particles could also become charged in our system, and,
consequently be the origin of the charging of the nanotubes, CO was
replaced by N.sub.2 (thereby preventing the formation of CNTs). Our
investigations carried out at temperatures from 25.degree. C. to
900.degree. C. showed that almost all the Fe particles (up to 99%)
were electrically neutral (table 2), which suggests that catalyst
particles are not directly involved in the observed charging of the
nanotubes.
To measure the mobility size distributions of the neutral aerosol
particles, the charged aerosol was filtered out by applying a
potential difference between electrodes in the ESF. The extracted
neutral aerosol particles were artificially charged using the
external bipolar charger (.sup.241Am) prior the mobility
distribution measurement by DMA. A peak with a mean equivalent
diameter of 5 nm was observed and assigned to Fe catalyst particles
that remain inactive for the growth of CNTs. Thus, these results
indicate that all the nanotubes were deposited in the ESF and,
hence, were electrically charged. Similar results were obtained at
800.degree. C. and 900.degree. C. (table 1).
TABLE-US-00001 TABLE 1 Charged fraction (N.sup.+/-) of CNTs,
synthesized using 53% CO and a heating power of 19 W, at different
reactor temperatures. (N.sup.+) and (N.sup.-) indicate the polarity
distribution of charged CNTs. Temperature (.degree. C.) N.sup.+/-
(%) N.sup.+ (%) N.sup.- (%) 700 99 47 53 800 99 48 52 900 97 41
59
TABLE-US-00002 TABLE 2 Charged fraction (N.sub.p.sup.+/-) of Fe
catalyst particles produced via HWG method in N.sub.2 atmosphere,
at different reactor temperatures. (N.sub.p.sup.+) and
(N.sub.p.sup.-) indicate the polarity distribution of charged
catalyst particles. Temperature (.degree. C.) N.sub.p.sup.+/- (%)
N.sub.p.sup.+ (%) N.sub.p.sup.- (%) 25 1 99 1 700 1 4 96 800 4 27
73 900 2 28 72
It is known that gas surface reactions may induce electronic
excitations at metal surfaces. When highly exothermic reactions
take place, these excitations may lead to the ejection of ions and
electrons from the surface. As a consequence, it can be speculated
that the exothermic CO disproportionation reaction needed for the
growth of CNTs might play a role in their electrical charging. In
an attempt to study it, experiments were carried out varying the CO
concentration. In order to quantitatively estimate the fraction of
charged CNTs (N.sup.+/-), mobility size distributions were measured
with the .sup.241Am bipolar charger prior the classifier. FIG. 10a
shows the comparison between the mobility size distributions of all
CNTs (ESF off) and the neutral CNTs (ESF on) at CO concentrations
of 27%, 34% and 53%. As is expected, the CNT concentration
increased with the concentration of carbon source (CO) introduced
into the reactor. At the concentration of 27%, the mobility size
distribution of all CNTs and the neutral fraction appeared to be
identical indicating that almost all CNTs are electrically neutral.
However, the fraction of neutral CNTs gradually decreased as the CO
concentration was increased. Thus, at 53% of CO, almost all the
CNTs were charged. FIG. 10b illustrates concisely the effect of the
CO concentration on the total fraction of charged nanotubes
(N.sup.+/-) and the concentration of the product.
In a similar manner, mobility distributions were also measured
varying the heating power applied to the wire from 16 W to 19 W
when the CO concentration was kept constant at 53%. Increasing the
power increases the concentration of CNTs, due to a higher
concentration of Fe catalyst particles produced. Consequently,
nanotube bundling increases. As can be seen in FIG. 11, the
fraction of the charged CNTs increased with the power applied to
the heated wire.
The results show that a higher concentration of CNTs leads to more
effective charging. This fact relates to the bundling of the CNTs,
since the likelihood for bundling increases with their
concentration in the gas phase. Accordingly, the natural charging
of the CNTs may happen in the process of formation of bundles. This
hypothesis was supported by TEM observation of the sample
containing charged CNTs, where only bundled CNTs were found (FIG.
9b).
In order to collect the neutral fraction of CNTs, the ESF was used
to filter out the charged CNTs. CNTs were synthesized using a
heating power of 16.5 W to maintain a low concentration of CNTs
and, thereby to minimize their bundling. At these experimental
conditions the fraction of charged CNTs was estimated to be around
12%. CNTs were collected directly from gas phase onto a TEM holey
carbon film substrate using a point-to-plate electrostatic
precipitator. TEM observations of the neutral CNTs revealed the
presence of only individual CNTs (FIG. 12a). The collection of the
whole product (i.e. without filtering charged CNTs out) revealed
the presence of both bundles and individual CNTs (FIG. 12b). This
indicates that individual CNTs were neutral whereas bundles were
charged.
The charging effect can be explained by the van der Waals energy
released during the CNT bundling. In order to minimize the total
free energy, CNTs form bundles consisting of individual tubes
located parallel to each other. This results in a relatively high
energy release: for example, the bundling of two armchair (10,10)
CNTs leads to the total energy decrease by as much as 95 eV/100 nm.
The bundle may be charged due to the emission of electrons and ions
via dissipation of the released van der Waals energy. The high
contact area to surface area ratio and high surface area to volume
ratio of CNTs likely allows a significant charging that would not
be detectable in large and/or low aspect ratio structures.
As the charging process due to bundling is directly related to the
high ratio of contact area to volume of these approximately
one-dimensional structures, the findings are applicable to any High
Aspect Ration Molecular Structures (HARM-structures) as mentioned
above.
Example 2
Separation of Bundled and Individual CNTs in the Gas Phase and
Separate Deposition Via Electrostatic Precipitation on
Polymer-based Substrate and Si.sub.3N.sub.4 Substrates
Bundled and individual CNTs were moved and thereby separated with
the method according to the present invention. The separated CNTs
were then separately deposited on a polymer-based substrate (SU-8,
10 .mu.m thick layer), with a degradation temperature of
.about.300.degree. C., and a Si.sub.3N.sub.4 substrate (119 .mu.m
thick layer). The deposition was carried out using an electrostatic
precipitator (FIG. 4). Atomic force microscopy (AFM) images
illustrated in FIG. 13a-b show the presence of individual CNTs,
which had been charged before the deposition, with diameters
ranging from 0.7 to 1.1 nm determined from the height measurements,
which is consistent with what is determined by TEM. In addition,
AFM images of individual CNTs collected onto and Si.sub.3N.sub.4
substrates (100 nm thick) are shown in FIG. 14.
Example 3
Separation of Bundled and Individual CNTs in the Gas Phase and
Separate Deposition Via Thermophoresis on a SiO.sub.2 Substrate
Bundled and individual CNTs were moved and thereby separated with
the method according to the present invention. The separated CNTs
were then separately deposited on a polymer-based substrate (SU-8,
10 .mu.m thick layer), with a degradation temperature of
.about.300.degree. C., and a SiO.sub.2 substrate. The deposition
was carried out using a thermophoretic precipitator (FIG. 6). An
atomic force microscopy (AFM) image illustrated in FIG. 15 show the
presence of individual CNTs.
Example 4
Deposition of Bundles of CNTs from the Gas Phase on a Silica
Substrate by Electrostatic Charging
Bundles of CNTs were produced in a CNT reactor using ferrocene and
carbon monoxide. The bundles were deposited from the gas phase onto
a silica substrate. The substrate was prepared beforehand so as to
have a local electrostatic charge by pressing the tip of an iron
pin to the substrate surface. Bundles of CNTs were deposited only
on the points where the pin pressure had been previously applied.
Resulting deposits are shown in FIG. 16.
The invention is not limited merely to the embodiment examples
referred to above, instead many modifications are possible within
the scope of the inventive idea defined in the claims.
* * * * *